An image display device such as a liquid crystal display or a projector is provided with a high pressure mercury lamp or the like as a light source. A high pressure mercury lamp is structured such that mercury or gas is confined in a glass tube. Thus, if the temperature of the lamp excessively rises, the glass tube will explode or quartz that makes up the glass tube will deform and thereby its permeability will deteriorate. To prevent such situations, image display devices that use a high pressure mercury lamp as a light source are generally provided with a cooling fan that cools the light source.
Some recent projectors that have a high pressure mercury lamp as a light source are provided with an energy saving mode that allows power supplied to the light source to be decreased to around several ten % of the maximum power (for example, around 75% to 80%). The energy saving mode might be set up, for example, by pressing a particular button mounted on the projector.
Generally, as power supplied to the light source decreases, the temperature of the light source becomes lower. Since the energy saving mode can decrease power supplied to the power source compared to the regular mode that causes the light source to be lighted at the maximum power, the energy saving mode can prevent a rise in the temperature of the light source and thereby can prolong the life of the light source.
However, projectors that are provided with the foregoing energy saving mode have the following problems.
It is known that when the temperature of a high pressure mercury lamp or the like as a light source excessively becomes low, mercury adheres to the inner surface of the glass tube, this phenomenon is known as the photo-darkening phenomenon.
In the energy saving mode, the temperature of the light source does not excessively rise compared to the regular mode. Thus, if the light source is cooled by a cooling fan in the same manner as in the regular mode, since the light source is excessively cooled, the photo-darkening phenomenon will occur.
Thus, if the energy saving mode is set up, it is necessary to decrease the amount of airflow of the cooling fan so as to prevent the occurrence of the photo-darkening phenomenon.
Patent Literature 1 discloses a technique that takes into consideration the temperature changes that occur in the light source when the light source is in the energy saving mode.
A projection type display device described in Patent Literature 1 has a light source, a sirocco fan, and a duct that guides cooling air generated by the sirocco fan to the light source. A control plate that controls the amount of airflow is rotatably supported in the duct so as to adjust the amount of airflow. When the angle of the airflow amount control plate changes, the area of the opening of the duct changes. As a result, the amount of airflow that flows in the duct increases or decreases. A control plate that controls the amount of airflow is rotated in association with a slide switch. The user can adjust the angle of control plate that controls the amount of airflow by using the slide switch.
When the power saving mode (corresponding to the foregoing energy saving mode) has been set up in the foregoing projection type display device, the user can operate the slide switch so as to decrease the amount of airflow supplied from the sirocco fan to the light source through the duct. Thus, excessive cooling of the light source can be prevented.